Frequency shift keying modulator and applications thereof

ABSTRACT

An FSK modulator and applications thereof are disclosed. The FSK modulator comprises a phase-locked loop, a frequency divider module, an image rejection mixer and a summing module. The phase-locked loop is operably coupled to generate a first oscillation from a reference oscillation. The frequency divider module is operably coupled to divide the first oscillation to produce a second oscillation. The image-rejection mixer is operably coupled to mix the second oscillation with a low intermediate oscillation to produce a mixed data signal, and the summing module is operably coupled to sum the mixed data signal with the first oscillation to produce an FSK modulated signal.

This invention is claiming priority to co-pending patent applicationentitled DIGITAL DEMODULATION AND APPLICATIONS THEREOF, having a filingdate of Nov. 14, 2001 and a Ser. No. 09/993,541.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to wireless communication systems and,more particularly, to radio frequency integrated circuits used in suchwireless communication systems.

BACKGROUND OF THE INVENTION

Communication systems are known to support wireless and wire-linedcommunications between wireless and/or wire-lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, et cetera, communicates directlyor indirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or multiple channels (e.g., one or moreof the plurality of radio frequency (RF) carriers of the wirelesscommunication system) and communicate over that channel or channels. Forindirect wireless communications, each wireless communication devicecommunicates directly with an associated base station (e.g., forcellular services) and/or an associated access point (e.g., for anin-home or in-building wireless network) via an assigned channel, orchannels. To complete a communication connection between the wirelesscommunication devices, the associated base stations and/or associatedaccess points communicate with each other directly, via a systemcontroller, via the public switch telephone network, via the internet,and/or via some other wide area network.

For each wireless communication device to participate in wirelesscommunications, it includes a built-in radio transceiver (i.e., receiverand transmitter) or is coupled to an associated radio transceiver (e.g.,a station for in-home and/or in-building wireless communicationnetworks, RF modem, etc.). As is known, the receiver receives RFsignals, demodulates the RF carrier frequency from the RF signals toproduce baseband signals, and demodulates the baseband signals inaccordance with a particular wireless communication standard torecapture the transmitted data. The receiver is coupled to an antennaand includes a low noise amplifier, one or more intermediate frequencystages, a filtering stage, and a data recovery stage. The low noiseamplifier receives inbound RF signals via the antenna and amplifiesthem. The one or more intermediate frequency stages mix the amplified RFsignals with one or more local oscillations to convert the amplified RFsignals into the baseband signals or intermediate frequency (IF)signals. The filtering stage filters the baseband signals or the IFsignals to attenuate unwanted out-of-band signals to produce filteredsignals. The data recovery stage recovers raw data from the filteredsignals in accordance with the particular wireless communicationstandard.

As is also known, the transmitter converts data into RF signals bymodulating the data to produce baseband signals and mixing the basebandsignals with an RF carrier to produce RF signals. The transmitterincludes a data modulation stage, one or more intermediate frequencystages, and a power amplifier. The data modulation stage converts theraw data into baseband signals in accordance with a particular wirelesscommunication standard. The one or more intermediate frequency stagesmix the baseband signals with one or more local oscillations to producethe RF signals. The power amplifier amplifies the RF signals prior totransmission via the antenna.

The local oscillations used in both the transmitter and in the receivermay be produced by the same or different local oscillation generators.Such a local oscillator may be in the form a phase locked loop (PLL),where the output frequency of the PLL is used as the local oscillation.Local oscillators used in direct conversion or very low intermediatefrequency (VLIF) transmitters and receivers include a PLL that producesan output frequency of approximately ⅔^(rd) of the desired localoscillation. To obtain the desired local oscillation, the outputfrequency of the PLL is divided by 2, creating a frequency ofapproximately ⅓^(rd) the desired local oscillation and then added to theoriginal ⅔^(rd) of the desired local oscillation. For example, as shownin FIG. 1, the PLL may produce an output oscillation of 1600 MHz, whichdivided by two equals 800 MHz, and, when mixed together, the resultinglocal oscillation of 2400 MHz is obtained.

As is also shown in FIG. 1, the local oscillation can be fed into afrequency shift keying (FSK) modulator (an I-Q mixer) in which an FSKbaseband signal is directly mixed with the local oscillation signal toform an FSK modulated signal. The FSK modulated signal is an RF signalthat can then be fed to, for example, a transmitter power amplifier.

A shortcoming with any I-Q mixer is keeping proper 90 degreephase-shifts on all ports of the mixer to prevent feed-through of theimage frequency, which is the opposite signed portion of the basebanddata signal riding on the local oscillation from that portion of thebaseband data signal being transmitted. In an on-channel FSK modulatorsuch as described above, the image frequency falls in-band (e.g., localoscillation frequency +/−baseband signal frequency), so excellentbalance must be maintained across frequency, temperature, and integratedcircuit process variation in order to attain an acceptable output signalfrom the FSK modulator. As frequencies get higher, the I-Q balance isdifficult to achieve, resulting in in-band image frequency leakage thatadversely affects the signal-to-noise ratio (SNR) of the modulated FSKsignal.

Further, prior to transmission of the modulated FSK signal, it is passedthrough a power amplifier (PA) that amplifies the signal by, forexample, 20-30 dB. Applying such gain to a high frequency signal canresult in feedback of the amplified modulated signal to the FSKmodulator, which corrupts the original modulated signal. Such corruptionresults because the feedback signal is phase-shifted from the originalmodulated signal, which disrupts the I-Q balance of the modulatedsignal, resulting in increased image frequency feed-through or otheradverse effects, such as variance in the signal amplitude. In an on-chipradio system there are typically several feedback paths that are layoutdependent. These feedback paths can cause varying amounts of phase andamplitude feedback into the FSK modulator. As a result, radio systemsincorporating a prior art local oscillation generation and highfrequency modulation scheme will suffer from in-band image frequencyleakage and feedback of the amplified FSK modulated signal into the FSKmodulator, resulting in a high signal-to-noise ratio and degraded RFsignals.

Therefore, a need exists for an FSK modulator and local oscillationgenerator that reduce and/or eliminate in-band image frequency leakageand feedback problems associated with the prior art.

BRIEF SUMMARY OF THE INVENTION

The FSK modulator and variations thereof of the present inventionsubstantially meet these needs and others. The FSK modulator comprises aphase-locked loop, a frequency divider module, an image rejection mixerand a summing module. The phase-locked loop is operably coupled togenerate a first oscillation from a reference oscillation. The frequencydivider module is operably coupled to divide the first oscillation toproduce a second oscillation. The image-rejection mixer is operablycoupled to mix the second oscillation with a low intermediateoscillation to produce a mixed data signal, and the summing module isoperably coupled to sum the mixed data signal with the first oscillationto produce an FSK modulated signal.

The phase-locked loop comprises a phase and frequency detection module,a charge pump, a loop filter, a voltage controlled oscillator (VCO), anda divider module. The phase and frequency detection module is operablycoupled to detect a phase and/or frequency difference between areference oscillation and a feedback oscillation to produce a differencesignal (e.g., charge up signal, charge down signal, zero signal). Theoutput of the phase and frequency detection module is provided to acharge pump, which creates a current signal therefrom. The loop filterfilters the current signal to produce a control voltage. The VCOreceives the control voltage and produces an output oscillationtherefrom, which may be the first oscillation and which is the inputoscillation of the frequency divider module and of the summing module.The frequency divider module receives the first oscillation and dividesthe first oscillation to produce a second oscillation, which is providedas an input to the image-rejection mixer.

The image-rejection mixer mixes the second oscillation with a lowintermediate oscillation received from, for example, a filtering/gainmodule in the radio transmission path, to produce the mixed data signal.The image-rejection mixer comprises first and second mixers, first andsecond phase-shift modules, and a mixer summing module. The first mixeris operably coupled to mix the second oscillation with the lowintermediate oscillation to produce a first mixed oscillation. The firstphase-shift module is operably coupled to phase-shift the secondoscillation to produce a phase-shifted second oscillation. Similarly,the second phase-shift module is operably coupled to phase-shift the lowintermediate oscillation to produce a phase-shifted low intermediateoscillation and the second mixer is operably coupled to mix thephase-shifted second oscillation with the phase-shifted low intermediateoscillation to produce a second mixed oscillation. The mixer summingmodule is operably coupled to sum the first mixed oscillation with thesecond mixed oscillation to produce the mixed data signal. The imagerejection mixer performs the phase shifts and mixing operations toensure that only the desired portion of the low intermediate oscillationis passed through to the power amplifier for transmission (i.e., itrejects the unwanted image frequency).

Because the frequency divider module of the embodiments of the FSKmodulator of this invention divides the first oscillation to a frequencyless than (e.g., one half) the frequency of the first oscillation priorto FSK modulation in the image-rejection mixer, in-band imagefeed-through is reduced, resulting in an FSK modulator output signalhaving an improved signal-to-noise ratio. Further, any feedback of themixed data signal back into the FSK modulator will happen at a frequencyoutside the frequency band of the oscillations within theimage-rejection mixer, and therefore will have little effect on themodulation properties of the mixed data signal.

The various embodiments of the FSK modulator of this invention may beused in a local oscillation module and/or in an IF mixing stage of aradio transmitter. By utilizing the FSK modulator in a radiotransmitter, the overall performance of the radio transmitter isenhanced because I-Q balance is easier to achieve in a lower frequencymodulation circuit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a prior art local oscillation generator/FSKmodulator;

FIG. 2 is a schematic block diagram of a wireless communication systemin accordance with the present invention;

FIG. 3 is a schematic block diagram of a wireless communication devicein accordance with the present invention;

FIG. 4 is a schematic block diagram of a local oscillation module inaccordance with the present invention;

FIG. 5 is a simplified schematic block diagram of an embodiment of anFSK modulator in accordance with the present invention;

FIG. 6 is a simplified schematic block diagram of an alternateembodiment of an FSK modulator in accordance with the present invention;

FIG. 7 is a schematic block diagram of an image-rejection mixer inaccordance with the present invention; and

FIG. 8 is a simplified schematic block diagram of an apparatus for FSKmodulation in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a schematic block diagram illustrating a communication system10 that includes a plurality of base stations and/or access points12-16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. The wireless communication devices 18-32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIG. 3.

The base stations or access points 12-16 are operably coupled to thenetwork hardware 34 via local area network connections 36, 38 and 40.The network hardware 34, which may be a router, switch, bridge, modem,system controller, et cetera provides a wide area network connection 42for the communication system 10. Each of the base stations or accesspoints 12-16 has an associated antenna or antenna array to communicatewith the wireless communication devices in its area. Typically, thewireless communication devices register with a particular base stationor access point 12-14 to receive services from the communication system10. For direct connections (i.e., point-to-point communications),wireless communication devices communicate directly via an allocatedchannel. Typically, base stations are used for cellular telephonesystems and like-type systems, while access points are used for in-homeor in-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio.

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, et cetera via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, digital receiver processingmodule 64, an analog-to-digital converter 66, a filtering/attenuationmodule 68, an IF mixing down conversion stage 70, a receiver filter 71,a low noise amplifier 72, a transmitter/receiver switch 73, a localoscillation module 74, memory 75, a digital transmitter processingmodule 76, a digital-to-analog converter 78, a filtering/gain module 80,an IF mixing up conversion stage 82, a power amplifier 84, a transmitterfilter module 85, and an antenna 86. The antenna 86 may be a singleantenna that is shared by the transmit and receive paths as regulated bythe transmit/receive switch 73, or may include separate antennas for thetransmit path and the receive path. The antenna implementation willdepend on the particular standard to which the wireless communicationdevice is compliant.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, digital intermediate frequency tobaseband conversion, demodulation, constellation demapping, decoding,and/or descrambling. The digital transmitter functions include, but arenot limited to, scrambling, encoding, constellation mapping, modulation,and/or digital baseband to IF conversion. The digital receiver andtransmitter processing modules 64 and 76 may be implemented using ashared processing device, individual processing devices, or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 64 and/or 76 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE 802.11a, IEEE 802.11b, Bluetooth, etcetera) to produce digital transmission formatted data 96. The digitaltransmission formatted data 96 will be a digital base-band signal or adigital low IF signal, where the low IF typically will be in thefrequency range of one hundred kilohertz to a few megahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogsignal prior to providing it to the IF mixing stage 82. The IF mixingstage 82 directly converts the analog baseband or low IF signal into anRF signal based on an output oscillation (first oscillation 126 and/orsecond oscillation 140) provided by local oscillation module 74. IFmixing stage 82 can comprise a combined local oscillator/image-rejectionmixer of the FSK modulator of the present invention. Local oscillationmodule 74 can comprise a receiver local oscillator and a transmitter VCOoutput oscillation source implemented in accordance with the teachingsof the present invention. Local oscillation module 74 and IF mixingstage 82 can be discrete components or can be implemented as a combinedoscillation-modulation stage for the transmit path. A separate localoscillation module 74 can be provided for the receiver section or thesame local oscillation module 74 can provide a local oscillation signalfor the receiver section and the transmit section. The power amplifier84 amplifies the RF signal to produce outbound RF signal 98, which isfiltered by the transmitter filter module 85. The antenna 86 transmitsthe outbound RF signal 98 to a targeted device such as a base station,an access point and/or another wireless communication device.

The radio 60 also receives an inbound RF signal 88 via the antenna 86,which was transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignal 88 to the receiver filter module 71 via the Tx/Rx switch 73,where the Rx filter 71 bandpass filters the inbound RF signal 88. The Rxfilter 71 provides the filtered RF signal to low noise amplifier 72,which amplifies the signal 88 to produce an amplified inbound RF signal.The low noise amplifier 72 provides the amplified inbound RF signal tothe IF mixing module 70, which directly converts the amplified inboundRF signal into an inbound low IF signal or baseband signal based on areceiver local oscillation 81 provided by local oscillation module 74,which may be implemented in accordance with the teachings of the presentinvention. The down conversion module 70 provides the inbound low IFsignal or baseband signal to the filtering/gain module 68. Thefiltering/gain module 68 filters and/or gains the inbound low IF signalor the inbound baseband signal to produce a filtered inbound signal.

The analog-to-digital converter 66 converts the filtered inbound signalfrom the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 3 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the digital receiver processing module 64, thedigital transmitter processing module 76 and memory 75 may beimplemented on a second integrated circuit, and the remaining componentsof the radio 60, less the antenna 86, may be implemented on a thirdintegrated circuit. As an alternate example, the radio 60 may beimplemented on a single integrated circuit. As yet another example, theprocessing module 50 of the host device and the digital receiver andtransmitter processing modules 64 and 76 may be a common processingdevice implemented on a single integrated circuit. Further, the memory52 and memory 75 may be implemented on a single integrated circuitand/or on the same integrated circuit as the common processing modulesof processing module 50 and the digital receiver and transmitterprocessing module 64 and 76.

FIG. 4 illustrates an embodiment of the local oscillation module 74 thatincludes a phase and frequency detection module 100, a charge pump 102,a loop filter 104, a voltage controlled oscillator (VCO) 106, and adivider module 108. The receiver local oscillation 81 may be generatedfrom the first oscillation 126 in a variety of embodiments. In oneembodiment, the receiver local oscillation 81 is directly produced fromthe first oscillation 126 via buffer 130. As one of average skill in theart will appreciate, an I and Q component for the receiver localoscillation 81 may be obtained by phase-shifting the I component of thereceiver local oscillation 81 by 90°. In this embodiment, thetransmitter local oscillation is generated from first oscillation 126 byIF mixing stage 82 in accordance with an embodiment of the presentinvention that will be discussed with regard to FIG. 5.

In an alternate embodiment, the receiver local oscillation 81 may beproduced by a plurality of logic gates. As shown, the first oscillation126 may be divided via a frequency divider module 134, which can be adivide-by-2 module, to produce a second oscillation 140 and thenmultiplied via mixer (multiplier) 136. The resulting oscillation frommixer 136 has a frequency that is 1-½ times the frequency of firstoscillation 126. From this increased oscillation the receiver localoscillation 81 is derived via buffer 138. As one of average skill in theart will appreciate, the first oscillation 126 may be phase-shifted by90° and the logic circuitry repeated to produce a Q component for thereceiver local oscillation 81. In this embodiment, second oscillation140 and first oscillation 126 are both provided to IF mixing stage 82 togenerate the transmitter local oscillation in accordance with theembodiment of the FSK modulator of this invention illustrated in FIG. 6.

The phase and frequency detection module 100 is operably coupled toreceive a reference oscillation 110 and a feedback oscillation 128 anddetect a phase and/or frequency difference between them. The referenceoscillation 110 may be produced by a crystal oscillator and/or anothertype of clock source. Phase and frequency detection module 100, loopfilter 104, VCO 106 and divider module 108 can be any such frequencydetection module, loop filter, VCO and divider module as known to thosein the art. Alternatively, they can be the like-named components asdescribed in co-pending patent application BP 2295, entitled LINEARIZEDFRACTIONAL-N SYNTHESIZER HAVING A GATED OFFSET, having a filing date of______/02, and a serial number of ______, which is hereby fullyincorporated by reference. The loop filter 104 provides the controlvoltage 124 to the voltage control oscillator 106. The voltage controloscillator 106 generates the first oscillation 126 based on the controlvoltage 124. The divider module 108 divides the first oscillation 126 byeither a fractional-N divider value or by a positive whole value toproduce the feedback oscillation 128.

FIG. 5 is a schematic block diagram of an embodiment of FSK modulator150 that includes a phase lock loop, a divide-by-two module, an imagerejection mixer 154, and a mixing module 160. FSK modulator 150 can beincorporated within or can be IF mixing stage 82 of FIG. 3. FSKmodulator 150 includes the phase-locked loop portion of localoscillation module 74 according to the first embodiment discussed withreference to FIG. 4. Local oscillation module 74 is operably coupled togenerate and then provide first oscillation 126 to divider module 152and to summing module 160. Divider module 152, which can be the same asdivider module 134, comprises a divide-by-2 module. Divider module 152is operably coupled to divide first oscillation 126 to produce secondoscillation 140. Image rejection mixer 154 is operably coupled to mixsecond oscillation signal 140 with a low intermediate oscillation 156 toproduce a mixed data signal 158. Summing module 160 is operably coupledto sum the mixed data signal 158 with the first oscillation 126 toproduce an FSK modulated signal 162.

The embodiments of the FSK modulator 150 of the present invention modifythe architecture of prior art local oscillation and modulation schemesby combining a local oscillation generator and an FSK modulator suchthat FSK modulation is performed at a lower frequency. By applying theFSK modulation at a lower frequency (e.g., 800 MHz), it is easier toachieve a tighter I-Q balance. The lower frequency FSK modulation alsoreduces or eliminates the possibility for on-frequency feedback of theFSK modulated signal 162, making the FSK modulator 150 more robust andlayout indifferent. Further, because the major components of the system(i.e., local oscillation generator and FSK modulator) are typicallyalready on-chip, an increase in circuit size is not required as noadditional components are added.

Returning to FIG. 5, first oscillation 126 can be, for example, a 1600MHz VCO output oscillation. In this case, second oscillation 140 will bean 800 MHz oscillation. Low intermediate oscillation 156 can typicallybe a +/−160 KHz baseband data signal comprising the FSK modulatedbaseband data being transmitted. This combination results in an 800 MHz+/−160 KHz mixed data signal 158 and in a 2400 MHz +/−160 KHz FSKmodulated signal 160. Mixed data signal 158 thus comprises a mixed localoscillation and baseband signal.

FIG. 6 is a schematic block diagram of an alternate embodiment of FSKmodulator 150. In this embodiment, FSK modulator 150 includes thephase-locked loop portion of local oscillation module 74 according tothe second embodiment discussed with reference to FIG. 4. Localoscillation module 74 is operably coupled to generate and then providefirst oscillation 126 to summing module 160 and to generate and providesecond oscillation 140 to image rejection mixer 154. The operation ofthe FSK modulator 150 of FIG. 6 is otherwise identical to that of theFSK modulator 150 illustrated in FIG. 5.

FIG. 7 is a schematic block diagram of image rejection mixer 154 ofFIGS. 5 and 6. Image rejection mixer 154 comprises a first mixer 170, afirst phase-shift module 172, a second phase-shift module 176, a secondmixer 178 and a mixer summing module 180. First mixer 170 is operablycoupled to mix the second oscillation 140 with the low intermediateoscillation 156 to produce a first mixed oscillation 174. Firstphase-shift module 172 is operably coupled to phase-shift the secondoscillation 140 to produce a phase-shifted second oscillation 182.Second phase-shift module 176 is operably coupled to phase-shift the lowintermediate oscillation 156 to produce a phase-shifted low intermediateoscillation 184. Second mixer 178 is operably coupled to mix thephase-shifted second oscillation 182 with the phase-shifted lowintermediate oscillation 184 to produce a second mixed oscillation 186.Mixer summing module 180 is operably coupled to sum the first mixedoscillation 174 with the second mixed oscillation 186 to produce themixed data signal 158. Phase-shift modules 172 and 176 can be ninetydegree phase-shift modules and, as one of average skill in the art willappreciate, are used to phase-shift the component oscillations of themixed data signal 158 to produce a Q component for mixed data signal158.

A further embodiment of the present invention can comprise an apparatusfor FSK modulation. As shown in FIG. 8, the apparatus 190 can comprise aprocessing module 192 and a memory 194. Processing module 192 may be asingle processing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory 194 may be a single memory device or aplurality of memory devices. Such a memory device may be a read-onlymemory, random access memory, volatile memory, non-volatile memory,static memory, dynamic memory, flash memory, and/or any device thatstores digital information. Note that when the processing module 192implements one or more of its functions via a state machine, analogcircuitry, digital circuitry, and/or logic circuitry, the memory storingthe corresponding operational instructions is embedded with thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. The memory 194 stores, and theprocessing module 192 executes, operational instructions correspondingto at least some of the steps and/or functions illustrated in FIGS. 3-7.

In a particular embodiment of apparatus 190, the memory 194 is operablycoupled to processing module 192 and includes operational instructionsthat cause the processing module 192 to generate the first oscillation126, divide the first oscillation 126 to produce a second oscillation140, image-rejection mix the second oscillation 140 with a lowintermediate oscillation 156 to produce a mixed data signal 158 and sumthe mixed data signal 158 with the first oscillation 126 to produce anFSK modulated signal 162. Further embodiments include the associatedmethods and applications of the FSK modulator of the present invention.

The embodiments of the FSK modulator of this invention can beincorporated, and it is contemplated that they will be used, in UHF andhigher communication systems. One application could be an RF applicationspecific integrated circuit (ASIC). For example, the Broadcom BCM2033single-chip Bluetooth solution, manufactured by Broadcom Corporation ofIrvine, Calif., can incorporate such an ASIC.

The preceding discussion has presented an FSK modulator and method forFSK modulation. Instead of separately modulating a high frequency (e.g.,2400 MHz) local oscillation, the FSK modulator of this inventioncomprises a combination of a local oscillation generator and amodulator. In particular, the FSK modulator performs the signalmodulation at a point where the VCO output oscillation has been divideddown (e.g., by two) and the frequency is lowest. The FSK modulator ofthis invention can therefore maintain good I-Q balance across frequency,temperature, and process better than prior art high frequency localoscillation and modulation schemes. As one of average skill in the artwill appreciate, other embodiments may be derived from the teaching ofthe present invention, without deviating from the scope of the claims.

1. A frequency shift keying (FSK) modulator comprises: a phase-lockedloop operably coupled to generate a first oscillation from a referenceoscillation; a frequency divider module operably coupled to divide thefirst oscillation to produce a second oscillation; an image-rejectionmixer operably coupled to mix the second oscillation with a lowintermediate oscillation to produce a mixed data signal; and a summingmodule operably coupled to sum the mixed data signal with the firstoscillation to produce an FSK modulated signal.
 2. The FSK modulator ofclaim 1, wherein the frequency of the first oscillation is twice thefrequency of the second oscillation.
 3. The FSK modulator of claim 1,wherein the frequency divider module is a divide by n module, where n isa positive whole number.
 4. The FSK modulator of claim 3, wherein n=2.5. The FSK modulator of claim 1, wherein the image-rejection mixerfurther comprises: a first mixer operably coupled to mix the secondoscillation with the low intermediate oscillation to produce a firstmixed oscillation; a first phase-shift module operably coupled tophase-shift the second oscillation to produce a phase-shifted secondoscillation; a second phase-shift module operably coupled to phase-shiftthe low intermediate frequency (IF) oscillation to produce aphase-shifted low IF oscillation; a second mixer operably coupled to mixthe phase-shifted second oscillation with the phase-shifted lowintermediate oscillation to produce a second mixed oscillation; and amixer summing module operably coupled to sum the first mixed oscillationwith the second mixed oscillation to produce the mixed data signal. 6.The FSK modulator of claim 5, wherein the first and second phase-shiftmodules are ninety-degree phase-shift modules.
 7. A method for frequencyshift keying (FSK) modulation, the method comprises: generating a firstoscillation; dividing the first oscillation by a divider value toproduce a second oscillation; image-rejection mixing the secondoscillation with a low intermediate frequency (IF) FSK modulated datasignal to produce a mixed data signal; and summing the mixed data signalwith the first oscillation to produce an FSK modulated signal.
 8. Themethod of claim 7, wherein the first oscillation is a 1600 MHzoscillation and wherein the second oscillation is an 800 MHzoscillation.
 9. The method of claim 7, wherein dividing comprisesdividing by n, where n is a positive whole number.
 10. The method ofclaim 9, wherein n=2.
 11. The method of claim 7, wherein image-rejectionmixing further comprises: mixing the second oscillation with the lowintermediate oscillation to produce a first mixed oscillation;phase-shifting the second oscillation to produce a phase-shifted secondoscillation; phase-shifting the low intermediate oscillation to producea phase-shifted low intermediate oscillation; mixing the phase-shiftedsecond oscillation with the phase-shifted low intermediate oscillationto produce a second mixed oscillation; and summing the first mixedoscillation with the second mixed oscillation to produce the mixed datasignal.
 12. The method of claim 11, wherein phase-shifting the secondoscillation comprises phase-shifting the second oscillation by ninetydegrees and wherein phase-shifting the low intermediate oscillationcomprises phase-shifting the low intermediate oscillation by ninetydegrees.
 13. An apparatus for frequency shift keying (FSK) modulation,the apparatus comprises: a processing module; and a memory operablycoupled to the processing module, wherein the memory includesoperational instructions that cause the processing module to: generate afirst oscillation; divide the first oscillation to produce a secondoscillation; image-rejection mix the second oscillation with a lowintermediate oscillation to produce a mixed data signal; and sum themixed data signal with the first oscillation to produce an FSK modulatedsignal.
 14. The apparatus of claim 13, wherein the frequency of thefirst oscillation is twice the frequency of the second oscillation. 15.The apparatus of claim 13, wherein dividing comprises dividing by n,where n is a positive whole number.
 16. The apparatus of claim 15,wherein n=2.
 17. The apparatus of claim 13, wherein image-rejectionmixing further comprises: mixing the second oscillation with the lowintermediate oscillation to produce a first mixed oscillation;phase-shifting the second oscillation to produce a phase-shifted secondoscillation; phase-shifting the low intermediate oscillation to producea phase-shifted low intermediate oscillation; mixing the phase-shiftedsecond oscillation with the phase-shifted low intermediate oscillationto produce a second mixed oscillation; and summing the first mixedoscillation with the second mixed oscillation to produce the mixed datasignal.
 18. The apparatus of claim 17, wherein phase-shifting the secondoscillation comprises phase-shifting the second oscillation by ninetydegrees and wherein phase-shifting the low intermediate oscillationcomprises phase-shifting the low intermediate oscillation by ninetydegrees.
 19. A radio comprising: a transmitter section operably coupledto convert outbound data into outbound radio frequency (RF) signalsbased on a transmitter local oscillation; a receiver section operablycoupled to convert inbound RF signals into inbound data based on areceiver local oscillation; a local oscillator operably coupled toproduce the receiver local oscillation, wherein the local oscillatorfurther comprises: a phase-locked loop operably coupled to generate afirst oscillation from a reference oscillation; a frequency dividermodule operably coupled to divide the first oscillation to produce asecond oscillation; and a mixer operably coupled to sum the secondoscillation with the first oscillation to produce the receiver localoscillation; and a frequency shift keying (FSK) modulator operablycoupled to produce the transmitter local oscillation and an FSKmodulated signal, wherein the FSK modulator comprises: the phase-lockedloop; the frequency divider module; an image-rejection mixer operablycoupled to mix the second oscillation with a low intermediateoscillation to produce a mixed data signal; and a summing moduleoperably coupled to sum the mixed data signal with the first oscillationto produce the FSK modulated signal.
 20. The radio of claim 19, whereinthe frequency of the first oscillation is twice the frequency of thesecond oscillation.
 21. The radio of claim 19, wherein the frequencydivider module is a divide by n module, where n is a positive wholenumber.
 22. The radio of claim 21, wherein n=2.
 23. The radio of claim19, wherein the image-rejection mixer further comprises: a first mixeroperably coupled to mix the second oscillation with the low intermediateoscillation to produce a first mixed oscillation; a first phase-shiftmodule operably coupled to phase-shift the second oscillation to producea phase-shifted second oscillation; a second phase-shift module operablycoupled to phase-shift the low intermediate oscillation to produce aphase-shifted low intermediate oscillation; a second mixer operablycoupled to mix the phase-shifted second oscillation with thephase-shifted low intermediate oscillation to produce a second mixedoscillation; and a mixer summing module operably coupled to sum thefirst mixed oscillation with the second mixed oscillation to produce themixed data signal.
 24. The radio of claim 23, wherein the first andsecond phase-shift modules are ninety-degree phase-shift modules.
 25. Aradio comprising: a transmitter section operably coupled to convertoutbound data into outbound radio frequency (RF) signals based on atransmitter local oscillation; a receiver section operably coupled toconvert inbound RF signals into inbound data based on a receiver localoscillation; a processing module; and a memory operably coupled to theprocessing module, wherein the memory includes operational instructionsthat cause the processing module to: produce the receiver localoscillation; and produce the transmitter local oscillation and an FSKmodulated signal, wherein producing the transmitter local oscillationand the FSK modulated signal comprises: generating a first oscillation;dividing the first oscillation to produce a second oscillation;image-rejection mixing the second oscillation with a low intermediateoscillation to produce a mixed data signal; and summing the mixed datasignal with the first oscillation to produce the FSK modulated signal.26. The radio of claim 25, wherein the frequency of the firstoscillation is twice the frequency of the second oscillation.
 27. Theradio of claim 25, wherein dividing comprises dividing by n, where n isa positive whole number.
 28. The radio of claim 27, wherein n=2.
 29. Theradio of claim 25, wherein image-rejection mixing further comprises:mixing the second oscillation with the low intermediate oscillation toproduce a first mixed oscillation; phase-shifting the second oscillationto produce a phase-shifted second oscillation; phase-shifting the lowintermediate oscillation to produce a phase-shifted low intermediateoscillation; mixing the phase-shifted second oscillation with thephase-shifted low intermediate oscillation to produce a second mixedoscillation; and summing the first mixed oscillation with the secondmixed oscillation to produce the mixed data signal.
 30. The radio ofclaim 25, wherein phase-shifting the second oscillation comprisesphase-shifting the second oscillation by ninety degrees and whereinphase-shifting the low intermediate oscillation comprises phase-shiftingthe low intermediate oscillation by ninety degrees.